Plasticized polyvinyl butyral sheet (PVB) is used in the manufacture of laminate structures such as, for example: windshields for vehicles including automobiles, motorcycles, boats and airplanes; homes and buildings; shelving in cabinets and display cases; and other articles where structural strength and laminate stability is desirable in a glass sheet. For the purposes of the present application, laminate stability refers to the ability of glass to remain adhered to PVB and/or the ability of the laminate layers to remain substantially together under harsh or even extreme circumstances. In some special applications, superior impact resistance and laminate stability is required, or highly preferable. For example, it can be preferred that laminates used in homes and other buildings withstand the harsh conditions prevalent in hurricanes, tornadoes, and/or severe wind storms.
A wide variety of glass laminates formed with PVB are known and described in U.S. Pat. No. 4,297,262; U.S. Pat. No. 4,230,771; and, British Patent 828,381. Typically, PVB is plasticized to have low stiffness and deform readily upon impact—which is an excellent property for automotive windshields wherein human impact is involved and passenger retention in a crash, and hence, reduction in fatality is desired. However, these are not the properties required for architectural windows exposed to high stresses, nor for side windows for automobiles and trucks that may be subjected to criminal actions. The properties of low stiffness and high elasticity limit performance when the laminate must provide intrusion resistance after the glass of the laminate has broken; for example, when a glass laminate is subjected to high wind load, and/or impact of flying debris as occurs in a hurricane, or where there is repeated impact to a window by a criminal attempting to break into a vehicle or structure. Conventional PVB laminates such as windshields or standard architectural laminated glass perform poorly in tests designed to evaluate the performance of a laminate under hurricane conditions, such as the Dade County, Fla. hurricane window system test protocol wherein there is a severe impact test followed by a pressure cycling test conducted on the shattered laminate.
Conventional PVB laminates can eventually fail in a hurricane when they are subjected to pressure loading and cycling. Failure can be due to either the large deformation of the polymer interlayer which can cause the laminate to pull out of the window frame, and/or due to the action of shards of broken glass which eventually cut into the PVB layer and allow air pressure or other threat to permeate the structure that the laminate is intended to protect. Conventional laminates can also be penetrated more readily with instruments used by a criminal attempting to gain entry through the laminate. The use of layers of PVB that are thicker than the standard laminate to gain more stiffness and cut-through resistance is impractical due to cost and the excessive thickness of the interlayer required. Similarly, the use of stiffer PVB of conventional thickness is difficult because the stiff PVB is more difficult to process, and there is considerable manufacturing yield loss.
Stiffer glass laminates have been made using interlayers other than PVB, such as polyurethanes and thermoplastic copolymers and all of these, including PVB, in combination with polyester film and polycarbonate films. Bolton et al, U.S. Pat. No. 4,663,228, for example, describes the use of an ionomer resin to form tough glass laminates.
There is an increased need for glass laminates for use as architectural windows that are resistant to the threats of wind storms and hurricanes, particularly in coastal areas. There is also a need for side windows for vehicles that are intrusion resistant. These glass laminates are required to have improved toughness and stability. They must also be easily fabricated, and have good optical properties—including color and clarity.
It is desirable to meet such needs with a PVB laminate that is tough, stable, and easily fabricated, and has good optical properties. These, and other objects of the invention will become apparent to the reader.